Power transmission device and power transmission-reception system

Abstract

A power transmission device has: a power transmission unit configured to perform wireless power transmission; a communication unit configured to perform wireless communication within a range wider than a power transmission possible range of the power transmission unit; and a power transmission control circuit configured to control power of wireless power transmission of the power transmission unit, wherein the power transmission control circuit controls the power of wireless power transmission of the power transmission unit according to a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than a threshold when the power transmission unit performs power transmission by first power, and a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by second power smaller than the first power.

The invention claimed is: 
     
       1. A power transmission device, comprising:
 a power transmission unit configured to perform wireless power transmission; 
 a communication unit configured to perform wireless communication within a range wider than a power transmission possible range of the power transmission unit; and 
 a power transmission control circuit configured to control power of wireless power transmission of the power transmission unit, wherein 
 the power transmission control circuit detects a first number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than a threshold from the power transmission device or other power transmission device when the power transmission unit performs power transmission by first power, and a second number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold from the other power transmission device when the power transmission unit does not perform power transmission or performs power transmission by second power smaller than the first power; obtains a number of the power reception devices receiving power equal to or more than the threshold from the power transmission device by subtracting the second number of the power reception devices from the first number of the power reception devices; and controls the power of wireless power transmission of the power transmission unit according to the number of the power reception devices receiving power equal to or more than the threshold from the power transmission device. 
 
     
     
       2. The power transmission device according to  claim 1 , wherein the power transmission control circuit detects a number of power reception devices existing in the power transmission possible range of the power transmission unit according to the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the first power, and the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by the second power, and controls the power of wireless power transmission of the power transmission unit according to the number of detected power reception devices. 
     
     
       3. The power transmission device according to  claim 1 , wherein the power transmission control circuit controls the power of wireless power transmission of the power transmission unit according to the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the first power, and the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission. 
     
     
       4. The power transmission device according to  claim 1 , wherein the power transmission control circuit controls the power of wireless power transmission of the power transmission unit according to the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the first power, and the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the second power. 
     
     
       5. The power transmission device according to  claim 1 , wherein the power transmission control circuit first detects the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the first power, thereafter detects the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by the second power, and controls the power of wireless power transmission of the power transmission unit according to a result of the detection. 
     
     
       6. The power transmission device according to  claim 1 , wherein the power transmission control circuit first detects the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by the second power, thereafter detects the number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit performs power transmission by the first power, and controls the power of wireless power transmission of the power transmission unit according to a result of the detection. 
     
     
       7. The power transmission device according to  claim 1 , wherein the power transmission control circuit regularly performs processing to control the power of wireless power transmission of the power transmission unit according to the number of power reception devices received by the communication unit when the power transmission unit performs power transmission by the first power, and the number of power reception devices received by the communication unit when the power transmission unit does not perform power transmission or performs power transmission by the second power. 
     
     
       8. The power transmission device according to  claim 1 , wherein the power transmission control circuit performs, several times at random cycles, processing to control the power of wireless power transmission of the power transmission unit according to the number of power reception devices received by the communication unit when the power transmission unit performs power transmission by the first power, and the number of power reception devices received by the communication unit when the power transmission unit does not perform power transmission or performs power transmission by the second power. 
     
     
       9. The power transmission device according to  claim 7 , wherein when the communication unit receives an indication of existence of another power transmission device inside the transmission possible range of the communication unit, the power transmission control circuit makes the cycles of the periodically performed processing be different from cycles of processing periodically performed by the other power transmission device. 
     
     
       10. A power transmission-reception system, comprising:
 a power transmission device; and 
 a power reception device, wherein 
 the power transmission device comprises: 
 a power transmission unit configured to perform wireless power transmission; 
 a communication unit configured to perform wireless communication within a range wider than a power transmission possible range of the power transmission unit; and 
 a power transmission control circuit configured to control the power of wireless power transmission of the power transmission unit, wherein 
 the power transmission control circuit controls the power of wireless power transmission of the power transmission unit according to a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than a threshold when the power transmission unit performs power transmission by first power, and a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by second power smaller than the first power, and 
 the power reception device has a communication unit transmitting to the power transmission device an indication of receiving power when power equal to or more than the threshold is received.